The name Dyson is as synonymous with good design as Apple is, with its founder, James Dyson, cleverly focusing on household appliances such as vacuum cleaners and hair dryers, whose quality is so good that customers do not mind paying top dollar for them. In his book Invention: A Life, publishing next week, Dyson, 74, explains not just how he built his empire but how his life is as much about failure as it is about success—and why that makes him happy.

​​JIM KELLY: It took you four years and 5,127 handmade prototypes of your famous cyclonic vacuum before you hit on the right model. What was the difference between prototype 5,126 and 5,127?